Recent pneumatic tires are required to have various kinds of improved performance, and their tread patterns are contrived to improve the performance. Heavy-duty tires are provided with tread patterns that improves traction performance.
For example, a heavy-duty pneumatic tire is known that improves in both traction performance in traveling on a bad road and wet performance in traveling at high speed (see Japanese Unexamined Patent Application Publication No. H09-136514A). The heavy-duty pneumatic tire includes, in a tread, at least one circumferential groove extending in the circumferential direction and a large number of lateral grooves connecting with the circumferential groove and disposed on both sides of the circumferential groove while being separated from each other in the circumferential direction. In the pneumatic tire:
(1) the circumferential groove extends in the circumferential direction in a tread central region that corresponds to 50% of the tread width;
(2) the depth of the circumferential groove is 5% of the tread width or greater; and
(3) the depth of at least lateral grooves disposed in both side sections of the tread among the lateral grooves is 109% of the depth of the circumferential groove or greater.
According to Japanese Unexamined Patent Application Publication No. H09-136514A, this configuration enhances both traction performance in traveling on a bad road and wet performance in traveling at high speed.
The above-described heavy-duty pneumatic tire can improve in traction performance in the terminal stage of wear. In such a heavy-duty pneumatic tire, the widths of blocks in a tread pattern may be increased in the tire width direction to further improve traction performance in some cases. In this case, the increased widths of the blocks in the tread central region readily increase ground contact pressure locally in the vicinities of edges of the blocks. If ends of belts in the tire width direction are disposed in substantially the same positions as the edges of the blocks in the tire width direction, the local increase in ground contact pressure applies great force to both ends of the belts in the tire radial direction and thus increases strain between belt layers. As a result, separation of belt edges readily occurs.
Especially large tires that are fitted to dump trucks traveling off-road, for example, on mines and have a size of, for example, 49 inches or greater are preferred to improve in both traction performance and belt durability by preventing separation of belt edges in view of effective use of the tires.